The purpose of this investigation is to evaluate a new restorative hybrid type restorative material (EXL 324) and to compare its wear characteristics with Z100 (3M Co) restorative material presently available in the dental market and having well characterized wear data. Ten z100 restorations and twelve experimental materials were randomly placed in the posterior teeth of six Macaca fascicularis monkeys. The two materials were clinically evaluated at 1 month and impressions taken at that time to measure the amount of wear that had occurred directly on the plastic casts of the restored teeth. The casts are evaluated for wear by 2 evaluators by viewing through a dissecting microscope in a double blind study. Further evaluations of the materials will be made at 3 months and at 6 monthly intervals thereafter. At one month, no discernible wear was observed in either of the two materials.;